The 20 deadliest aliens in science fiction

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If there's one thing science fiction has taught us over the years, it's that first contact is probably not going to go very well. Now, that may be us humans, a very war- and violence-oriented species, projecting ourselves on other potential inhabitants of the universe, but there are definitely plenty of examples out there for us to peruse in which the aliens among us are deadly and terrifying killers.

But who's the baddest of them all? Well, with Alien: Covenant around the corner, we take a look at the history of invading forces in the worlds of science fiction in TV, film, comics and games and try to determine who has the highest body count.

War of the Worlds: Martians

Approximate Kill Count: Shockingly Low

One of the most famous alien invasion stories has a shockingly low body count, as only around 50 died when the Martians invaded in War of the Worlds. The potential was very high, but thanks to Earth bacteria, we all came out okay from this one.

Aliens: Xenomorphs

Approximate Kill Count: Full Planets, but only around 50 on screen

Another case of a much smaller on-screen kill count than you may expect – just over 50 people have been killed on screen by the Alien xenomorphs. However, the implication (and expanded universe) is that these aliens are very deadly, having wiped out full planets. Still, if we're going by just what we've actually seen, they're all bark and very little bite.

Marvel Studios: Chitauri

Approximate Kill Count: Hundreds, but Fewer Than 1,000

This one is heavily contested, but in-universe, we've had numbers of both in the 80s and "Hundreds" listed or mentioned on screen. The latter is a little more believable; yes, the Avengers were actively working during the Battle of New York to save people while also fighting the Chitauri, but New Yorkers are way too stubborn to have evacuated that quickly. Trust us, we've been in NYC for blizzard and hurricane evacuation orders; a 10% compliance rate might be high in some cases.

DC Comics: Darkseid and the Apokoliptians

Approximate Kill Count: Hundreds, Low Thousands

Another one that may surprise people with how few they've actually killed is Darkseid and his army from Apokolips. While his Parademons sure look scary and deadly as they fly through the air with their claws and teeth and razor-sharp metal wings, they don't seem to pull off all that much in the actual killing department. Darkseid is more interested in controlling all life than ending it, after all, as opposed to his Marvel counterpart we'll get to later ...

DC Films: Kryptonians

Approximate Kill Count: 129,000

The other recent big-screen battle in superhero films took place in Man of Steel, where the rogue Kryptonian criminals did some major damage. While filmmakers tried to call the kill count "around 5,000," one population expert said that based on the buildings damaged in the battle between Superman and Zod, plus the gravity weapon, the number is more like 129,000 deaths. Now we have to see what Aquaman thinks of a giant Kryptonian weapon falling into one of his oceans …

Independence Day Aliens

Approximate Kill Count: Low Millions

The initial attack from the aliens in Independence Day killed millions in major population centers, but an ongoing evacuation effort prevented that number from being in the tens or even hundreds of millions. Comparatively speaking, these guys weren't all that effective in doing much more than inspiring humanity!

Starship Troopers: Arachnids

Approximate Kill Count: Contested, Possibly Billions

The books and movie universe are definitely different here, but in the books the Arachnids have several worlds, at least a few of which were conquered. This one is nearly impossible to come to a consensus count to, but there's no question that their swarm mentality, something we've seen across many mediums and universes in other aliens, would result in near-total population death of any populated planet they visit.

Falling Skies: The Espheni

Approximate Kill Count: 6 Billion+ (Most of Human Population)

When the Espheni came to Earth, they wiped out the vast majority of the human population. Based on a current population of around 7.5 billion, that means well over six billion died. With the enslaving of the remainder, the dead may have been the lucky ones.

DC Comics: Dominators

The second DC Comics example here is the Dominators, who led the alien consortium in an invasion against Earth (and were recently seen on TV in the CW four-show crossover). While they only kidnapped/enslaved/killed a few thousand humans, their reputation was that if they couldn't dominate a world, they'd simply destroy it. They've done it to many planets over the years, which means they've taken out billions. They're also one of the most scary-looking humanoid designs out there.

Invader Zim: Irken Empire

Approximate Kill Count: High Billions (Multiple planets)

Doomy doom doom doom doomy doom doom. That's what the Irken bring, and they've destroyed several planets. Lucky for Earth, our Invader was a little less destructive and a little more hilarious. They're also by far the most adorable killers on this list. Doom.

BSG: Cylons

Approximate Kill Count: Tens of Billions (Most of population of Multiple Colony Planets)

All of this has happened before … but when Battlestar Galactica was rebooted, things kicked off with one hell of a bang, as the humans' entire nuclear arsenal was set off on themselves, killing at least tens of billions in one fell swoop, stranding the vast majority of the survivors in a fleet in space.

Star Trek: Species 8472

Approximate Kill Count: Tens of Billions (Borg alone)

This Star Trek Voyager species comes from "liquid space," a side-dimension of sorts, which they've presumably completely conquered. When the Borg try to assimilate Species 8472, the species strikes back, killing tens of billions of the Collective. It's highly probable this is not the only population they've decimated.

Halo: The Flood

Approximate Kill Count: 23 billion (During Human-Covenant War alone)

Ah, the big twist of The Flood – like the other 'swarm' aliens on this list, their devastation is nearly unstoppable thanks to sheer numbers. Thanks to some of the side-fiction of the Halo universe, this video game alien's body count is numbered, at least during the events of the games, at around 23 billion.

Mass Effect: The Reapers

Approximate Kill Count: Hundreds of Billions

While the Reapers didn't wipe out all life in the Milky Way Galaxy like they intended, they definitely destroyed entire worlds and colonies and caused the near-extinction of several sentient races in their time. The new explorers in Andromeda going up against the Kett don't know how good they have it compared to Commander Shepard and her crew back home.

Dragon Ball Super: Beerus

Approximate Kill Count: Hundreds of Billions

Okay, this one is cheating a tiny bit, as Beerus is technically a god, not an alien per se (but hey, he lives on another planet out on space, so it works for us). Still, he's a great modern example of destruction and extinction being used as a pure plot device. The implication is that Beerus has been committing some straight-up genocide periodically for all of time. We see him literally split a planet in half with a snap in his earliest moments.

Warhammer 40k: Tyranid Hive Fleet

Approximate Kill Count: Hundreds of Billions

Perhaps the ultimate realization of the 'hive alien' or 'alien swarm' (sorry, Marvel's Annihilation Wave), the Tyranid Hive Fleet(s) from this tabletop game are unparalleled in their devastating power. They're said to have killed hundreds of billions on conquered (or rather, devoured) worlds and if left unchecked could essentially eat the entire galaxy. Yowza.

Doctor Who: Time Lords

Approximate Kill Count: Trillions

The Time Lord known as the Doctor is the hero of Doctor Who, but the Time Lords are also arguably the worst villains in the series. During the Time War, they wiped out entire races like the Zygons and Gelth, and it culminated in the end of the Time Lords themselves, the Gallifreyans, as well as an estimated hundreds of billions, if not trillions of Daleks. Do not get on the bad side of a Time Lord, folks.

Star Wars: Yuuzhan Vong

Approximate Kill Count: 365 trillion

The primary villains of the "New Jedi Order" phase of the Star Wars Expanded Universe, the Yuuzhan Vong were alien invaders from outside of the main Star Wars galaxy. Their power was utterly devastating, they hated mechanical technology and couldn't be sensed by the Force. That all led to the near-total destruction of the New Republic in those old Legends tales, with a death toll of 365 trillion given in-universe, essentially 49,000 Earths. That may seem like a lot, but astronomers estimate that there may be anywhere from 18-40 billion Earth-like planets in habitable zones of stars in the Milky Way alone, so it's actually very plausible. Regardless, that's a lot of dead folks, but luckily that continuity was wiped out, so we can only assume they're all okay now.

Marvel Comics: Thanos, the Mad Titan

Approximate Kill Count: Literally Half the Universe

The top two deadliest aliens both come from comics, and are both primarily solo acts. First, from Marvel Comics is Thanos, who will star as the primary villain in Avengers: Infinity War and presumably again in Avengers 4. This biggest of big bads, when he got his hands on the Infinity Gauntlet and all six Infinity Gems (Stones in the MCU), he wiped out half of the entire Universe's population in an instant. If you accept that there are a theorized number of planets in the septillions in the universe, and lowball it that 18% (18 billion out of the 100 billion Milky Way planets for our sake) are habitable, and then take Earth's 7.5 billion population, that's a universal population of 1.35e+33, and a death toll of 6.75e+32 – around 7 dectillion dead – a number so large it's essentially inconceivable. Yeah, Thanos is a killer, and he does it all in the name of love (he just happens to be in love with the personification of Death).

DC Comics: Krona of the Maltusians

Approximate Kill Count: Several Entire Universes

The only one that could possibly outdo Thanos, then, is Krona. One of the Maltusians, a race that became the "Guardians of Oa/the Universe" – the little blue guys who make and give out Green Lantern Rings – Krona was obsessed with figuring out, and witnessing, how the universe began. He was so obsessed that he wound up paging through universes like a book, destroying them in his wake. Yes, he killed multiple entire universes (after first killing mere individual worlds as shown here). While other characters have done similar feats, he's the alien example of this, and therefore has a truly countless death toll on his résumé.